I think that the threshold is far lower than that, actually. If they did to an American plane what they did to the Russian plane, that would be a tipping point. Easier said than done, obviously, because our security situation is qualitatively different from Egypt's. But, it's not ironclad by any stretch. And if there's anything that makes people in the US jittery, it's airplanes. One bomb, even an unsuccessful bombing attempt where the attacker gets through TSA screening, would be a major game changer, I think. In the few years after 9/11 there were at least two failed bombing attempts on planes coming from Europe to the US, and people were able to keep their cool for the most part, so hopefully I'm not correct.I don't think it's a stretch of the imagination to think that all it would take is an ISIS coordinated attack on American soil for the shit to hit the fan.